The solid freeform fabrication method known as selective laser sintering is a layered manufacturing technique that is capable of fabricating complexly shaped objects directly from computer models (CAD) using a laser to selectively fuse powder particles together. Selective laser sintering is one of several commercially available solid freeform fabrication technologies that can build objects layer by layer. However, presently there are no solid freeform fabrication technologies that can build objects with functionally tailored heterogeneous or varying material compositions.
While conventional selective laser sintering technology allows a user to create a variation in material composition along the build direction by intentionally layering powders of different compositions along the depth of an selective laser sintering powder supply bin, in order to deposit a true three-dimensional composition gradient varying in both the build direction as well as across the plane of each layer, a different type of powder deposition mechanism from that which is currently used is required. A typical solid freeform fabrication process is illustrated in FIG. 1.
Solid freeform fabrication processes rely on the concept of layer-by-layer material addition to selected regions. A computer 10 is used to generate a model 11 that serves as the basis for making a replica of a desired structure. The computer-generated model 11 is mathematically sliced into thin cross-sectional layer representations via an automatic process planner 12 to form a sliced model 13. Each slice is created in the material of choice to build a complete, three-dimensional object. To build the physical shape, the material of each layer is selectively added or deposited and fused to the previous layer in an automated fabrication machine 14.
FIG. 2 illustrates the well known solid freeform fabrication technique of selective laser sintering. In the selective laser sintering process, a layer of powdered material 16 from a powder supply bin 18 is applied to a deposition bed 20. The powder 16 is spread over the top surface of a partially manufactured growing sintered prototype 22 by a roller mechanism 24. A laser 26 is then used to selectively scan the layer of powder 16 to fuse portions of the powder 16 to form a particular cross-sectional layer of the model 13. Subsequent layers are fused together in the same manner.
The laser beam 26 is directed using computer-controlled mirrors 28 which are themselves directed by the automatic process planner 12. Any unfused material 30 remains in place as a support structure of the sintered prototype 22. After each layer of powder 16 is deposited, an elevator platform 32 lowers the growing sintered prototype 22 by the thickness of the layer deposited and the next layer of powder 16 is deposited. When the shape of the prototype 22 is completely formed, the prototype 22 is separated from the unfused material 30. The sintered prototype 22 produced using this traditional selective laser sintering technique has a homogenous composition.
In contrast to present selective laser sintering techniques, Applicants' invention uses selective laser sintering to build heterogeneous functionally tailored composite devices. In order to accomplish Applicants' goal of using selective laser sintering to build such composite devices, powders of different compositions must be deposited in prescribed patterns layer by layer as the particular device is manufactured.